如何在游戏中显示SPARQL查询的输出！查看？

Question

我正在编写一个应用程序，用户可以在其中上传.rdf文件，然后在其中执行SPARQL查询。现在，我陷入了如何格式化查询结果的困境。例如：ASK-Query输出一个布尔值，SELECT-Query返回一个ResultSet。CONSTRUCT和DESCRIBE返回一个新的RDF图。

如何在表单中获取给定查询的结果，以便将其传递给我的视图？在那里，我希望打印出一个HTML表格。

为了更好地理解我的问题，我创建了这个简约的代码示例：

import java.io.InputStream;

import com.hp.hpl.jena.*;

public class playground {

    public static void main(String[] args) {

      InputStream in = FileManager.get().open("vc-db-1.rdf");
      Model model = ModelFactory.createDefaultModel();
      model.read(in, null);

      String queryStringSelect = "SELECT ?subject ?predicate ?object WHERE { ?subject ?predicate ?object }";
      String queryStringAsk = "ASK WHERE { ?subject ?predicate ?object }";
      String queryStringDescribe = "DESCRIBE * WHERE { ?subject ?predicate ?object }";
      String queryStringConstruct = "CONSTRUCT { ?subject ?predicate ?object } WHERE { ?subject ?predicate ?object }";

      QueryExecution qe = QueryExecutionFactory.create(queryStringDescribe,
        model);
      Query q = QueryFactory.create(queryStringDescribe);

      int queryType = q.getQueryType();
      switch (queryType) {
      case Query.QueryTypeAsk:
          boolean b = qe.execAsk(); // Result that has to be formatted
          ResultSetFormatter.outputAsTSV(System.out, b);
          break;
      case Query.QueryTypeConstruct:
          model = qe.execConstruct(); // Result that has to be formatted
          model.write(System.out);
          break;
      case Query.QueryTypeDescribe:
          model = qe.execDescribe(); // Result that has to be formatted
          model.write(System.out);
          break;
      case Query.QueryTypeSelect:
          ResultSet results = qe.execSelect(); // Result that has to be
                 // formatted
          ResultSetFormatter.outputAsTSV(System.out, results);
          break;
      }

      model.close();
      qe.close();

    }

}

可以从以下位置下载提及的.rdf文件：http://jena.apache.org/tutorials/sparql_data/vc-db-1.rdf

Answer 1

我终于找到了答案：

我使用ByteArrayOutputStream并使用各种model.write()函数来完成剩下的工作。对于SELECT-Query，我使用文本表示，因为提供的ResultSetFormatter.outputAsRDF()让我可以返回许多无用的东西。不管怎样，下面是相关的代码

ByteArrayOutputStream baos = new ByteArrayOutputStream();
...
int queryType = q.getQueryType();
switch (queryType) {
case Query.QueryTypeAsk:
    boolean b = qe.execAsk();
    ResultSetFormatter.outputAsRDF(baos, notation, b);
    retval = baos.toString();
    break;
case Query.QueryTypeConstruct:
    model = qe.execConstruct();
    model.write(baos, notation);
    retval = baos.toString();
    break;
case Query.QueryTypeDescribe:
    model = qe.execDescribe();
    model.write(baos, notation);
    retval = baos.toString();
    break;
case Query.QueryTypeSelect:
    ResultSet results = qe.execSelect();
    ResultSetFormatter.out(baos, results);
    retval = baos.toString();
    break;
}